| Pile-soil interaction analysis is an important part of the bearing capacity study of pile foundation.The response of pile-soil system will change due to the variable load form,especially under seismic load,whose direction and magnitude continuously change with time.It is more difficult to capture the response of pile-soil system under such a complex load path as the principal stresses change in both magnitude and direction.Moreover,the seismic load causes the soil deformation first,and then drives the pile to move.Therefore,site response analysis is the premise of the pile-soil interaction analysis.The finite element method(FEM)is widely used to simulate the macroscopic mechanical behavior of large-scale geotechnical engineering numerical models,although the function for meso-mechanism analysis of soil is relatively limited.Sand is a typical granular material.The discrete element method(DEM)is good at simulating torsion and contact of granular materials.So it has a high accuracy in reproducing the mesoscopic behavior of sand.Moreover,DEM can capture the stress-strain characteristics of sand without complex constitutive equations.However,DEM is too timeconsuming analyzing the model of project scale,which limits its application in macroscopic model.Therefore,a multi-scale coupling method for complex load paths is proposed in this paper combined the advantages of both FEM and DEM.The FEM-DEM multi-scale coupling method simulates the macroscopic behavior through FEM,and uses DEM as representative volume element(RVE)to simulate the constitutive relation of Gaussian points in FEM.The main research contents and conclusions of this paper are as follows:(1)The multi-scale coupling computing platform is proposed combining the finite element software ABAQUS and discrete element software LIGGGHTS by Python in Linux.The construction process of platform is introduced.At the same time,in order to make the mechanical behavior of sand can be accurately reflected by the coupling model,the sensitivity analysis is carried out for the parameters of discrete element sand sample.The results show that the calculation accuracy of discrete element samples is proportional to the number of particles.The void ratio of the samples increases with the increase of the friction coefficient and Young’s modulus of particles during consolidation.When the friction coefficient exceeds about 0.5 or the particle strength exceeds 800 MPa～1000 MPa,the void ratio tends to be stable.(2)Triaxial compression test is simulated on the single Gaussian point coupling model using the above multi-scale coupling method,and compared with that based on DEM.The results show that the coupling method can reproduce the mechanical behavior of sand.The simulation results have high accuracy.(3)The site response under one-dimensional shaking and two-dimensional shaking is studied in both macro and micro scale using the above multi-scale coupling method.Twodimensional shaking test was designed to simulate complex load paths.The results show that the multi-scale coupling platform can capture the macroscopic mechanical behavior and mesostructural changes of the site under shear waves.The influence of complex load path effect on the site response is discussed.(4)Based on the principle of p-y curve method and the above site response calculation results,a single pile-soil spring model is established in Open Sees for pile-soil interaction analysis.The results show that the complex load path effect has obvious influence on the site response and pile-soil interaction.Combined with the macroscopic and meso-scale results of site response,the complex load path effect may increase site settlement,increase pile top acceleration and pile bending moment,enhance dynamic response.The above examples show that the FEM-DEM multi-scale coupling method this paper proposed can accurately simulate the mechanical behavior of sand and the pile-soil interaction behavior under complex load path,which provides a new tool for the macroscopic and mesoscopic analysis of sand and the analysis of pile-soil interaction. |
